Do you provide engineering work through LinkedIn? LinkedIn is a live resume that sometimes reminds you about a work anniversary. If you're a P.E. in all 50 states or in one, putting P.E. at the end of your name and leaving it at that isn't wrong, illegal, or worth reading the LinkedIn user...
Unless you affix your seal and signature to your work, its not legally bound to you. That is the point of the stamp and license number. LinkedIn is social media and not much else...